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LOP and ROP OPs


INA201

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This is one of the things that Transition Training is good for...

There are lots of good details written by good people....

But... not all of them apply directly to a TC’d engine...

Dave M. Is a great resource...

Mapalog is a great resource...

Reading MS is a great resource...

GSXer is a great resource...

Make sure the resource’s info applies to your engine before using it...

 

Some pilots may need more training than others... it is easy to miss something and think it applies... or so much information available it is easy to leave out a step or get the order mixed up...

Ask lots of questions...and take good notes...

Don’t be surprised after you have all the good hardware.... training is still very helpful.

PP thoughts only, not a CFI...

Best regards,

-a-

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8 hours ago, carusoam said:

This is one of the things that Transition Training is good for...

There are lots of good details written by good people....

But... not all of them apply directly to a TC’d engine...

Dave M. Is a great resource...

Mapalog is a great resource...

Reading MS is a great resource...

GSXer is a great resource...

Make sure the resource’s info applies to your engine before using it...

 

Some pilots may need more training than others... it is easy to miss something and think it applies... or so much information available it is easy to leave out a step or get the order mixed up...

Ask lots of questions...and take good notes...

Don’t be surprised after you have all the good hardware.... training is still very helpful.

PP thoughts only, not a CFI...

Best regards,

-a-

Amigo, you are preaching to the choir!

When I bought my 231, my insurance carrier insisted on a minimum of 15 hours dual instruction since I was  low time retractable gear pilot. I hired David McGee at All American for that, and had a BFR a couple moNths ago with another Mooney-savvy CFI last fall. But engine management in the 231 is a black box to most people who don’t have one! GSXer pointed me to a CFI I can rely on for the best info and instruction in this area. 

Edited by CoffeeCan
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20 hours ago, Niko182 said:

From what ive heard, 40 to 50 rop is the worst place for an engine to be.

It depends.

An ideal engine would fire the spark plugs at top dead center (TDC) and the mixture would ignite all at once and expand and push the piston down. But in a real engine the mixture takes time to burn. The flame fronts begin at the spark plugs and progress to meet in the middle. During this time the piston is moving -- first up toward TDC and then down again. This means that the size of the combustion chamber is shrinking and then expanding while the mixture is burning. Together these effects result in the combustion chamber pressure rising to a peak and then dropping off. It's the overall average pressure (engineers call it brake mean effective pressure, BMEP) that does the work of pushing the piston, not just the peak pressure. But where in the cycle the peak is located and the height of the peak have a lot to do with efficiency and engine stresses. There is an optimum point for the peak which is generally somewhere in the vicinity of 15 degrees after TDC where the engine generates the most torque and this will be the most efficient place to operate (maximum torque for a given amount of fuel). Generally higher peaks transfer more heat to the cylinder heads. Also, if the peak is too high and especially when combined with high CHTs, the anti-knock value of the gasoline will be exceeded and detonation may occur.

Since magento timing is fixed and propeller efficiency considerations limit our range of rpm, our primary means of affecting peak pressure is the mixture control. Leaner mixtures burn slower and move the peak later in the cycle. This has the effect of lowering the peak and making the engine more efficient. It also reduces power output because the BMEP is reduced. At low power settings (let's say 65% and below) the heat load on the engine is less and you can run the mixture wherever you want. At full power, full rich is required. In between, your best proxy to determine that your peak pressure is not too high is CHT. High CHT weakens the metal in the cylinder heads, stresses the valves and decreases their life and also (and more importantly) reduces the detonation margin.

So what about 50 ROP? Well, on the good side, when you want more power, it provides a compromise between best power and best economy (usually peak or leaner) mixtures. On the bad side it is the mixture that produces the highest peak pressure and the highest CHT. Is this really bad? Well, it depends on the power demanded from the engine. At 65%, no problem. At higher powers, it's OK if the CHTs stay in check (Lycoming's long-standing recommendation has been 435 for high performance cruise and 400 for economy cruise. I'd go with 400F max). If the CHTs get too high, you have to reduce power or adjust the mixture richer or leaner. High CHT and high power is what you really want to avoid.

Remember, back when all the engine and airplane operator manuals were written we didn't have such good instrumentation and gas was cheap. Simple rules were created to make engine operation simple and safe for us amateur pilots (The professionals had gads of engine instruments and a flight engineer to keep things in check). Now we have better instrumentation, gas and engines are expensive and we know more. This has opened up a whole range of possibilities. The best advice from those that have a lot of experience is to understand what happens when you move the red knob and then make up your own simple rules based on what you want to accomplish. Mike Busch for instance clearly states that he is more interested in longevity than speed and he runs his engines at 65% or less and LOP. His engines typically make it well past TBO. Others have discovered that they can cruise at 80%+ power when well LOP and still have cool CHTs. 

Hope this helps.

Skip

 

 

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On 1/18/2020 at 12:12 PM, CoffeeCan said:

Amigo, you are preaching to the choir!

 

You figured me out!  :)

I spend a fare amount of time trying to understand what MSers are looking for...

Then connecting them to the people that have answers...

The rest of the time I’m preaching to the choir, and cheering Go Mooney!

Best regards,

-a-

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  • 4 weeks later...
On 1/10/2020 at 1:33 PM, gsxrpilot said:

You don't just have a turbo, you have a Rocket! My 252 turbo runs very well LOP. My GAMI spread is about .4 and I can get to 20 or 30 degrees lean without any roughness. I hear the Rockets are more difficult to get to run well LOP. The one Rocket pilot that does LOP very well is Lacee @RocketAviator. He's not on this forum much anymore, but maybe the ping will get him to chime in.

I only do LOP at 65% power or less. That way I can actually run right AT peak and the power is low enough that I don't have to worry about harming the engine.

Oh, and my TIT does come down off the peak when I'm LOP. I'm running about 1530 or so TIT and my hot cylinder is usually below 330.

@gsxrpilot nice numbers for me to aspire to with my Encore. Now that some basic mechanical and avionics work is complete, I'm working on fine tuning calibration.

LASAR completed some significant avionics upgrades over the past months. Among them - EDM730 is now fully wired for all parameters including fuel flow. First GAMI sweeps came in at 0.4-0.6gph - right on the edge. Even so, LOP at 65% has TITs in the 1611-1625 range - a little warm for my liking. I suspect many of my plugs are misfiring based on an inflight mag test, so I'm having them replaced. Old plugs were 12 years old and had >500 hours; other engine data shows oscillating CHTs on 4 of 6 cylinders, especially when engine is hot and ROP. Hoping a more reliable spark will smooth ROP and LOP engine running and maybe reduce TIT LOP. If not, will get a leaner #6 cyl fuel injector (it's 0.3-0.44gph richer than the other 5 cylinders). 

Getting 3PG flying in good working order and smoothly running has been quite a project!

Edited by bcbender10
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